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BackgroundFusions in cases of reduced bone density are a tough challenge. As not only does bone quality have an influence on force transmission, these forces must be bridged for much longer time, as a fusion takes longer than in bone-healthy patients. However, cage subsidence or displacement results to loss of reposition and pain. From a biomechanical point of view, the majority of current studies have focussed on the range of motion or have shown test setups for single component tests. Definite setups for biomechanical testing of the primary stability of a 360° fusion using a screw rod system and cage on the osteoporotic spine are missing. The aim of this study is to develop a test stand to provide information about the bone-implant interface under reproducible conditions.MethodsAfter pre-testing with artificial bone, human functional spine units were tested with 360° fusion in TLIF technique. The movement sequences was conducted in flexion, extension, right-left lateral bending and right-left axial rotation on an osteoporotic human model.ResultsDuring the testings of human cadavers, 4 vertebrae were fully tested and were inconspicuous even after radiological and macroscopic examination. 1 vertebra showed a subsidence of 2mm and 1 vertebra had a cage collapsed into the vertebra.ConclusionsThis setup is suitable for biomechanical testing of cyclical continuous loads on the osteoporotic spine. The embedding method is stable and ensures a purely monosegmental setup. The optical monitoring provides a very accurate indication of cage movement, which correlates with the macroscopic and radiological results.

Introduction Acetabular fractures pose high demands on the surgeon and in the case of osteosynthetic treatment, anatomical reconstruction has the highest priority to achieve a good outcome. However, especially in older patients with poor bone quality, even anatomical reconstruction is no guarantee for a good clinical outcome and may nevertheless end in early osteoarthritis. Primary arthroplasty therefore has an increasing importance in the treatment of these patients. The aim of this study was to biomechanically compare fracture gap displacement and failure load as an assessment measure of the primary stability of conventional plate osteosynthesis with the treatment using a sole multi-hole cup for acetabular fractures. Methods Six hemi-pelvises each with anterior column and posterior hemi-transverse (ACPHT) fracture were treated with either plate osteosynthesis or a multi-hole cup. The tests were carried out in a standardised test set-up with cyclic loading in various stages between 150 N and 2500 N. The fracture gap displacement was recorded with optical 3D measuring and the failure load was determined after the cyclic measurement. Results With increasing force, the fracture gap displacement increased in both procedures. In each group there was one treatment which failed at the cyclic loading test and a bone fragment was broken out. The primary stability in arthroplasty was comparable to that of the standard osteosynthesis. Conclusions The results found seem promising that the primary arthroplasty with a sole multi-hole cup and corresponding screw fixation achieves an initial stability comparable to osteosynthesis for typical ACPHT fractures. However, further clinical studies are needed to prove that the cups heal solidly into the bone.

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